1. Field of the Invention
The present invention relates to a liquid container in which a liquid such as ink is contained in a flexible bag, and more particularly to technique for detecting an amount of remaining liquid in the container in a liquid ejection device.
2. Related Art
An ink container for supplying ink to an ink jet recording head mounted on a carriage via a passage maybe roughly classified into two types of ink containers; a first type of ink container in which ink is directly contained in a hard case, and a second type of ink container in which ink is contained in a flexible bag, and the bag is put in a hard case according to the necessity.
When the ink jet recording head is caused to perform ink ejecting operation such as printing in a state that no ink is supplied to the recording head, the recording head is fatally damaged. To avoid the damage, the management of the remaining ink amount is of particular importance.
There is a proposal of the management of the remaining ink amount (Japanese Patent Publication No. JP-A-2001-146019). The proposed management is implemented in the first type of ink container; ink is directly contained in a hard case. As described in the JP-A-2001-146019, a window, for example, is formed in a region located in level lower than a liquid level of ink in the ink container so that a vibration characteristic receives the ink. A piezoelectric vibrator is fixed to the window directly or with a vibration plate interposed therebetween. An amount of remaining ink is detected from a variation of a residual vibration due to an increase of an area of the vibration plate where it contacts with air, with a variation of a liquid level of the ink.
In the second type of ink container, viz., the ink bag is used as the ink container, even when ink is consumed, the ink bag is merely shrunk, and no air enters the ink bag. Accordingly, the surround of the vibration plate is not replaced with air. Accordingly, it is impossible to directly apply the method of detecting the amount of remaining ink to the second type of ink container.
German Unexamined Patent Publication No. 19917229 discloses the ink pack which is made of flexible material, and attached with a sensor capable of an ink level of the ink in the ink pack. A method for detecting an amount of ink in the ink pack and a specific structure of the sensor are not disclosed.